The subject invention pertains to a cellulosic composite which uses an improved binding composition. More specifically, the invention pertains to a cellulosic composite which employs as a binder an improved curable composition comprising an addition product of an amine and a reactant in the form of a amino-amide intermediate. An aldehyde or ketone is added to the amino-amide to form a composition which upon curing is capable of forming a water-insoluble polymer composition.
Composite wood products prepared from various lignocellulosic materials (e.g., wood) have been known for centuries, although industrial production began only about a century ago. Among other things, these products offer a relatively low cost and a reasonably high strength to weight ratio. Consequently, they are used in a number of capacities including interior and exterior construction, furniture and even marine applications. Several distinct composite wood products exist including plywood, oriented strand board, particleboard and medium density fiberboard (MDF).
One type of molded composite article is a cellulosic (or woody) composite which includes man-made boards of bonded wood sheets and/or lignocellulosic materials, commonly referred to in the art by the following exemplary terms: fiberboards such as hardboard, medium density fiberboard, and softboard; particleboards such as chipboard, flakeboard, particleboard, strandboard, and waferboard. Wood composites also include man-made boards comprising combinations of these materials. These wood composites can be used as columns, floors, ceilings, walls, doors, siding and stairs in the construction of homes, offices, and other types of buildings, as well as furniture components, such as chairs, tables, countertops, cabinets, and cabinet doors, for example.
Many different methods of manufacturing wood composites are known in the art such as, for example, those described in U.S. Pat. No. 6,841,231. The principal processes for the manufacture of fiberboard include: (a) wet felted/wet pressed or “wet” processes; (b) dry felted/dry pressed or “dry” processes; and, (c) wet felted/dry pressed or “wet-dry” processes. Synthetic binder resins, such as amino resins, urea-formaldehyde resins, phenol-formaldehyde resins, or modified phenol-formaldehyde resins, are often used as binders in these processes. Other binders include, but are not limited to, starches, asphalt, and gums.
Products such as particleboard and MDF are typically prepared from an adhesive resin composition and comminuted lignocellulosic materials such as wood flakes or wood fibers. The manufacture of particleboard and MDF begins with the reduction of the wood particles to a particulate size or a fiber, which will occasionally be referred to herein as a furnish. This furnish is then blended with an adhesive resin and transported to a forming device, which shapes the mixture into a mat. The mat is then loaded into a heated press that shapes and pressurizes the mat to a desired thickness. The pressure and heat together act to cure the resin, which bonds the mixture into a panel or board. Bonding performance is affected by, among other factors, the amount and type of resin, the curing time and the curing pressure.
In U.S. Pat. No. 7,217,458, OSB boards are discussed. Oriented strand board (“OSB”) is commercially available. OSB material generally is formed of multiple layers of wood “flakes” or “strands” bonded together by a resin binder under heat and compression to provide a unitary board structure. The flakes are made by cutting logs into thin slices with a knife edge oriented parallel to the length of a debarked log. The cut flakes are broken into narrow strands generally having lengths oriented parallel to the wood grain that are larger than the strand widths.
In one common fabrication of oriented strand board, the flakes generally are first dried to remove water, and are then coated in a blender with a thin layer of binder and sizing agent. The coated flakes are then spread on a conveyor belt to provide a surface ply or layer having flakes oriented generally in line with the conveyor belt, then one or more plies that will form an interior ply or plies of the finished board is (are) deposited on the surface ply such that the one or more plies is (are) oriented generally perpendicular to the conveyor belt. Then, another surface ply having flakes oriented generally in line with the conveyor belt is deposited over the intervening one or more plies having flakes oriented generally perpendicular to the conveyor belt. The resulting structure includes plies having flakes oriented generally perpendicular to a neighboring ply insofar, such as for each surface ply and the adjoining interior ply. The layers of oriented “strands” or “flakes” are finally exposed to heat and pressure to bond the strands and binder together to form a consolidated board structure. Other variations on this basic manufacturing scheme also are known. The resulting product is then cut to size and shipped. Typically, the resin and sizing agent comprise less than 10% by weight of the oriented strand board.
The predominant resin systems in the composite wood industry are urea-formaldehyde (UF) and phenol-formaldehyde (PF) resins. Although these formaldehyde-based resins perform consistently, the physical properties of composite wood products prepared with formaldehyde-based resins are often unsatisfactory. For example, the internal bond strength of composite wood products frequently renders them unfit for certain demanding applications. In addition, such products are commonly susceptible to significant swelling upon exposure to moisture. As a consequence of these and other factors, composite wood products prepared with UF and PF resins are often less robust than desired.
Currently, alternatives to formaldehyde-based resins are being investigated. See, for example U.S. Pat. No. 6,822,042. The potentially attractive alternatives include resin systems that employ isocyanates. Such resin systems have been shown to impart markedly improved physical properties to composite wood products. For example, concentrated isocyanate-based resins increase bonding strength, and therefore offer a more robust and durable composite wood product. Unfortunately, isocyanate-based resins also have several known drawbacks that have limited their commercial utility. First, isocyanates are relatively expensive as compared to other resin materials. Consequently, concentrated isocyanate-based resins are uneconomical as compared with traditional formaldehyde-based resins. Second, unlike UF and PF resins, isocyanates are highly reactive with water. Consequently, isocyanates react quickly with any water present in either the wood furnish or the resin itself. This limits both the shelf-life of the resin and the lignocellulosic materials with which it can be used. Third, isocyanates are toxic and their use creates environmental, health and industrial hygiene concerns. Thus, process safety considerations influence against the use of concentrated isocyanate-based resins.
Accordingly, in one aspect the present invention provides a novel cellulosic composite comprised of a unique formaldehyde free binder.
Another aspect of the invention provides a novel cellulosic composite with a binder which provides the possibility of lower binder usage, the possibility of overall lower energy consumption, increased sustainability of the raw materials utilized in the formation of the binder, considerable reduction in the use of petroleum based ingredients and improved overall economics.
Still another aspect of the present invention is to provide a cellulosic composite which employs a unique binder having improved economics, improved health, safety and environment factors by eliminating formaldehyde and isocyanate while also enjoying improved physical properties.
These and other aspects of the present invention will become apparent to the skilled artisan upon a review of the following description and the claims appended hereto.